The human heart generally includes four valves. Of these valves, a most critical one is known as the mitral valve. The mitral valve is located in the left atrial ventricular opening between the left atrium and left ventricle. The mitral valve is intended to prevent regurgitation of blood from the left ventricle into the left atrium when the left ventricle contracts. In preventing blood regurgitation the mitral valve must be able to withstand considerable back pressure as the left ventricle contracts.
The valve cusps of the mitral valve are anchored to muscular wall of the heart by delicate but strong fibrous cords in order to support the cusps during left ventricular contraction. In a healthy mitral valve, the geometry of the mitral valve ensures that the cusps overlie each other to preclude regurgitation of the blood during left ventricular contraction.
The normal functioning of the mitral valve in preventing regurgitation can be impaired by dilated cardiomyopathy caused by disease or certain natural defects. For example, certain diseases may cause dilation of the mitral valve annulus. This can result in deformation of the mitral valve geometry to cause ineffective closure of the mitral valve during left ventricular contraction. Such ineffective closure results in leakage through the mitral valve and regurgitation. Diseases such as bacterial inflammations of the heart or heart failure can cause the aforementioned distortion or dilation of the mitral valve annulus. Needless to say, mitral valve regurgitation must not go uncorrected.
One method of repairing a mitral valve having impaired function is to completely replace the valve. This method has been found to be particularly suitable for replacing a mitral valve when one of the cusps has been severely damaged or deformed. While the replacement of the entire valve eliminates the immediate problem associated with a dilated mitral valve annulus, presently available prosthetic heart valves do not possess the same durability as natural heart valves.
Various other surgical procedures have been developed to correct the deformation of the mitral valve annulus and thus retain the intact natural heart valve function. These surgical techniques involve repairing the shape of the dilated or deformed valve annulus. Such techniques, generally known as annuloplasty, require surgically restricting the valve annulus to minimize dilation. Here, a prosthesis is typically sutured about the base of the valve leaflets to reshape the valve annulus and restrict the movement of the valve annulus during the opening and closing of the mitral valve.
Many different types of prostheses have been developed for use in such surgery. In general, prostheses are annular or partially annular shaped members which fit about the base of the valve annulus. The annular or partially annular shaped members may be formed from a rigid material, such as a metal, or from a flexible material.
While the prior art methods mentioned above have been able to achieve some success in treating mitral regurgitation, they have not been without problems and potential adverse consequences. For example, these procedures require open heart surgery. Such procedures are expensive, are extremely invasive requiring considerable recovery time, and pose the concomitant mortality risks associated with such procedures. Moreover, such open heart procedures are particularly stressful on patients with a compromised cardiac condition. Given these factors, such procedures are often reserved as a last resort and hence are employed late in the mitral regurgitation progression. Further, the effectiveness of such procedures is difficult to assess during the procedure and may not be known until a much later time. Hence, the ability to make adjustments to or changes in the prostheses to obtain optimum effectiveness is extremely limited. Later corrections, if made at all, require still another open heart surgery.
An improved therapy to treat mitral regurgitation without resorting to open heart surgery has recently been proposed. This is rendered possible by the realization that the coronary sinus of a heart is near to and at least partially encircles the mitral valve annulus and then extends into a venous system including the great cardiac vein. As used herein, the term “coronary sinus” is meant to refer to not only-the coronary sinus itself but in addition, the venous system associated with the coronary sinus including the great cardiac vein. The therapy contemplates the use of a device introduced into the coronary sinus to reshape and advantageously affect the geometry of the mitral valve annulus.
Devices of this type generally include an elongated flexible member having a cross sectional dimension for being received within the coronary sinus of the heart and an anchor at each end. When placed in the coronary sinus, the devices reshape the mitral valve annulus, or at least a portion of it, to promote effective valve sealing action and eliminate or reduce mitral valve regurgitation. Device structures and methods of implanting the same are fully described, for example, in copending U.S. patent applications Ser. No. 10,011,867, filed Dec. 5, 2001, titled ANCHOR AND PULL MITRAL VALVE DEVICE AND METHOD, Ser. No. 10/066,426, filed Jan. 30, 2002, titled FIXED LENGTH ANCHOR AND PULL MITRAL VALVE DEVICE AND METHOD, Ser. No. 10/142,637, filed May 8, 2002, titled BODY LUMEN DEVICE ANCHOR, DEVICE AND ASSEMBLY, and Ser. No. 10/331,143, filed Dec. 26, 2002, titled SYSTEM AND METHOD TO EFFECT THE MITRAL VALVE ANNULUS OF A HEART. The disclosures of the foregoing patent applications are incorporated herein by reference.
The foregoing therapy has many advantages over the traditional open heart surgery approach. Since the therapy may be employed in a comparatively noninvasive procedure, mitral valve regurgitation may be treated at an early stage in the mitral regurgitation progression. Further, the therapy may be employed with relative ease by any minimally invasive cardiologist. Still further, since the heart remains completely intact throughout the procedure, the effectiveness of the procedure in reducing mitral valve regurgitation may be readily determined, such as by echocardiography or fluoroscopy. Moreover, should adjustments be deemed desirable, such adjustments may be made during the procedure and before the patient is sent to recovery.
Unfortunately, the human anatomy does impose some obstacles to this recently proposed procedure for treating mitral regurgitation. More specifically, the coronary sinus/great cardiac vein runs in the atrioventricular groove between the left atrium and left ventricle. The left circumflex artery originates from the left main coronary artery and courses within the atrioventricular groove. One to three large obtuse marginal branches extend from the left circumflex artery as it passes down the atrioventricular groove. These principal branches supply blood to (perfuse) the lateral free wall of the left ventricle. In approximately 15% of the population, the left circumflex artery is a dominant source of blood to the left posterior descending artery for perfusing and supporting the viability of the left ventricle. When the circumflex artery is superior to the coronary sinus, the obtuse marginal branches extending towards the ventricular wall may run either underneath the coronary sinus or above the coronary sinus. Hence, when placing a mitral valve therapy device in the coronary sinus/great cardiac vein of a patient, great care must be taken to prevent occlusion of this coronary artery system.
Even when great care is taken to avoid occlusion of the coronary arteries during placement of a prosthetic device in the cardiac venous system, arterial perfusion of the heart may be unacceptably reduced by the device. Copending U.S. patent application Ser. No. 10/366,585, filed Feb. 12, 2003, and titled METHOD OF IMPLANTING A MITRAL VALVE THERAPY DEVICE, the disclosure of which is incorporated herein by reference, discloses a method of optimizing patient outcome while performing a procedure in the venous system of a patient's heart. As described in that patent application, a mitral valve therapy device is placed within the coronary sinus adjacent to the mitral valve annulus of the patient's heart. The effectiveness of the device in reducing mitral valve regurgitation is evaluated, and arterial perfusion of the heart is assessed. Depending on the outcome of the evaluation and assessment, the position of the device may require adjustment or the device may have to be removed. Removal of the device may be advisable, for example, if exchange to a device of different dimension would be more appropriate for that patient.